Doctors come and Doctors go, but the BBC will reveal the identity of the next Doctor Who star in a special live event later today. The current Doctor, Matt Smith, has filmed his last Doctor Who special, which will air later this year. Unlike most roles in television, the mantle of The Doctor is passed from one actor to the next every few seasons, and it’s been going on for a long time.

There have been 11 different Doctors over the years, stretching all the way back to the early 1960s. The show ran more or less continuously until 1989, when it took a long hiatus. There was a TV movie in the mid 90s, but we don’t like to talk about that. Doctor Who was revived in 2005 with Christopher Eccleston playing the main role.

Within Doctor Who mythos, The Doctor is able to generate a total of 12 times, becoming a totally different person. This allows the show to continue on with a different actor in the starring role, but The Doctor is fast running out of lives. Occasional suggestions that there is no limit have been laughed off as jokes by showrunners. When the new actor (whoever it is) takes over the show, that will be the 12th Doctor. Meaning the BBC only has one more regeneration after that, if it wants to stick to the original rules.

Matt Smith took over the show from the much beloved David Tennant in 2010. He was at first seen by many fans as too young for the role, but seems to have won most Whovians over. Quite a few names have been floated as possible choices for the new Doctor, with 55 year-old Peter Capaldi emerging as the odds-on favorite. Ben Daniels from the BBC series Cutting It and Chiwetel Ejiofor (Children of Men) have also been rumored.

We’re going to find out soon who gets to take the Tardis for a spin. Whoever it is, they’ll have some big shoes to fill (and they’re bigger on the inside). The announcement will be broadcast on BBC and BBC America at 7PM London time, or 2PM ET.

Update: The BBC has announced that Peter Capaldi will indeed be the new Time Lord.